Problem: Tiffany did 8 more push-ups than Luis at night. Luis did 20 push-ups. How many push-ups did Tiffany do?
Explanation: Luis did 20 push-ups, and Tiffany did 8 more than that, so find the sum. The sum is $20 + 8$ push-ups. She did $20 + 8 = 28$ push-ups.